Exemplary embodiments of the invention generally relate to a rotary wing aircraft, and more particularly, to a vibration control or suppression system in a rotary wing aircraft.
Rotary wing aircraft, or rotorcraft, can generate significant vibratory responses during operation. The primary source of such vibration is that generated by the main rotor system rotating at the blade passing frequency and the periodic loads acting on the rotor blades. Forces and moments are transmitted through the gearbox into the airframe, resulting in airframe vibration.
Active vibration control (AVC) systems that are characterized by anti-vibration actuators mounted in the fuselage or on or very near the helicopter main transmission to suppress otherwise high levels of vibration are often heavier than desirable, resulting in a reduced payload of the aircraft. For systems intended to generally completely suppress the aircraft vibration, six or more anti-vibration actuators, typically the heaviest components in AVC systems, are required. Thus it is desirable to reduce the weight and number of AVC actuators.
For rotor-based anti-vibration systems, the corresponding rotor-based actuators are typically oscillated at frequencies of the fuselage or other vibrations to be suppressed. In general, rotor-based systems cannot totally suppress all of the vibratory loads originating from the main rotor(s) either because the number of distinct load directions is greater than the number of controls or because the power or amplitude needed to provide complete suppression of the vibration by the rotor-based system alone is onerous. Also, the rotor-based system might be tasked with improving rotor efficiency or some other attribute and not tasked with reducing vibration. As a result, the residual vibration may thus “leak” into the airframe and cause unwanted vibration.